Abstract: A very compact flow loop for circulating gas through a pulsed laser or other pulsed discharge device is disclosed. An apparatus, having greater resistance to flow and shock wave propagation in the upstream direction, preferentially converts energy from the pulsed discharge residue into flow energy and causes flow through the discharge region in the desired downstream direction. The large available work in the discharge residue lets the efficiency of the conversion apparatus be very low and yet still provide sufficient flow power to circulate gas for purging a conventional flow loop without using a separate input of power to drive the purge flow. Moderate conversion efficiency provides sufficient flow power to allow compact, high loss components to be used for a very compact flow loop with no external flow circulation power and no rotating components.